In the propylene oxide styrene monomer (POSM) process, methyl oxirane (propylene oxide) and ethenyl or vinyl benzene (styrene monomer) are co-produced. Molecular oxygen is reacted with ethylbenzene to form .alpha.-hydroperoxy ethylbenzene which is then subsequently reacted with propene to form propylene oxide and .alpha.-hydroxyethylbenzene, also known as methylbenzyl alcohol.
After removing the more volatile propylene oxide, the methylbenzyl alcohol is dehydrated to water and styrene monomer. These are co-distilled overhead and condensed into a water/oil separator, where the water forms a separate phase and is drained. The crude styrene phase is then extracted in a caustic wash drum with 5 to 10% of an aqueous caustic solution containing about 2 to 3% NaOH, sometimes with about an equal amount of a caustic solution recycled to remove phenolic byproducts of the above-described oxidation and epoxidation reactions.
The caustic extracted styrene is then rinsed in a water wash drum with 5 to 10% fresh water, also sometimes with about an equal amount recycled, to remove residual caustic and phenate salts from the crude styrene prior to distillation. Typically, the temperature of the extraction is about 100 to 110.degree. F. The pH in the second stage is about 11.5 and in the first stage is about 14.
The present inventor has discovered a means to improve this extraction process while minimizing residual carryover of caustic and phenates to the styrene distillation towers. This method also helps eliminate the production and disposal as toxic waste of stable dispersion layers which otherwise accumulate in separation vessels.